The proposed study applies social-interactional and biological perspectives to better understand how interpersonal conflict (IC) relates to physiological stress, engagement in health risk behaviors, and internalizing symptoms in adolescents. Despite considerable evidence that IC is a stressor for adolescents and relates to their overall adjustment, little is known about the interrelationships among IC, physiological stress, health risk behaviors, and internalizing symptoms. The overarching goal of this study is to advance understanding of how adolescents' experiences of IC with parents, peers, and dating partners are linked separately and cumulatively with diurnal patterns of physiological stress, engagement in a variety of dangerous health risk behaviors, and adolescents' internalizing symptoms. The proposed study aims to (a) examine the relation between current experiences of IC, previous IC, and diurnal patterns of hypothalamic-pituitary- adrenocortical (HPA) axis activity as indexed by cortisol; (b) examine how IC and health risk behaviors, including both sensation-seeking behaviors (e.g., reckless driving) and stress-dampening behaviors (e.g. alcohol use), relate to diurnal HPA axis activity; and (c) explore the associations among IC, HPA axis activity, health risk behaviors, and internalizing symptoms to gain a more thorough understanding of how to integrate these constructs within the context of adolescent development. The proposed study builds on an ongoing longitudinal project that provides multiple waves of data of IC across adolescence in addition to prospective daily measurements for 10 consecutive days. This study goes beyond the parent project by assessing diurnal patterns of HPA activity through a series of saliva samples, assayed for cortisol, on 3 of the 10 days of daily data, and by assessing IC immediately preceding the saliva collections. The proposed study also provides an assessment of wide-ranging health risk behaviors 6 months following the other assessments. The proposed project will better delineate the nature and impact of different types of IC (physical, psychological, and electronic forms of aggression) in different relationships (parents, peers, and dating partners) for female and male adolescents. With attention to bi-directional effects, analyses will explore additive and interactive influences among IC, health risk behaviors, HPA activity, and internalizing symptoms. Analyses also explore competing hypotheses about sensitization versus attenuation in response to IC as manifested in physiological activity. With IC relatively commonplace in the lives of adolescents, the question here is whether IC alone or in combination with various patterns of physiological activity helps explain adolescents' engagement in dangerous or health compromising behaviors and adolescents' development of internalizing symptoms. PUBLIC HEALTH RELEVANCE: Health risk behaviors and internalizing symptoms, which are common among adolescents, can result in serious and sometimes fatal consequences and lead to a lower quality of life. Healthy People 2010 Health Objectives include the reduction of adolescents' health risk behaviors, such as tobacco use and unprotected sex, and increase their overall quality of life and access to mental health treatment. Understanding how interpersonal relations, in combination with biological reactions such as diurnal HPA activity, affect adolescents' engagement in risk behaviors and experience of internalizing symptoms would inform prevention and intervention practices, reducing the harm caused by these common behaviors and psychological symptoms.